1. Field of the Invention
The present invention relates to a display device and a method of driving a display device, and more particularly, to a liquid crystal display (LCD) device and a method of driving an LCD device.
2. Discussion of the Related Art
In general, an LCD device includes two substrates that are spaced apart and face each other, and a liquid crystal material layer interposed between the two substrates. Each of the substrates includes electrodes that face each other, wherein a voltage supplied to each of the electrodes induces an electric field to the liquid crystal material layer. Accordingly, alignment of liquid crystal molecules of the liquid crystal material layer is changed by varying an intensity or direction of the induced electric field, thereby changing light transmissivity through the liquid crystal material layer. Thus, the LCD device displays images by varying the induced electric field.
The LCD device displays images using a plurality of pixels arranged in a matrix configuration. In general, each of the pixels has red, green, and blue sub-pixels that produce red, green, and blue colored light, respectively.
Currently, an RGBW-type LCD device has been used, wherein pixels include red, green, blue, and white sub-pixels to additionally produce white colored light to increase luminance of displayed images. Accordingly, color purity (or color saturation) of displayed images including the white colored light is less than a color purity of images displayed without the white colored light. In addition, the color purity of the images displayed using the white colored light includes halftones of the original images displayed without the white colored light.
By way of example, JP11-321901 discloses an LCD device and driving method thereof for preventing reduction of original images when the display device further has a white sub-pixel. According to JP11-321901, ratios of red, green, and blue color input luminance data corresponding to original images are the same as ratios of red, green, and blue color output luminance data corresponding to displayed images as following:Ri:Gi:Bi=(Ro+Wo):(Go+Wo):(Bo+Wo)wherein Ri, Gi, and Bi are red, green, and blue input data, respectively, and Ro, Go, Bo, and Wo are red, green, blue, and white output data, respectively. Accordingly, although the LCD device further includes a white sub-pixel, color purity of original images remains unchanged.
FIG. 1 is a diagram demonstrating a relationship between gray level and luminance of RGB, W, and RGB+W gamma curves according to the related art. As shown in FIG. 1, the RGB gamma curve represents red, green, and blue data, the W gamma curve represents white data, and the RGB+W gamma curve represents red, green, blue, and white data when gray levels are between 0 to 255.
In FIG. 1, the RGB gamma curve is produced when a gamma value is about 2.5, and red, green, and blue data have gamma values of about 2.5. However, as the white sub-pixel is added, gamma values are changed from about 2.5 to about 2.8. Accordingly, the RGB+W gamma curve is a combination of the RGB and W gamma curves.
As shown in FIG. 1, when the gray level is more than about a 150th level, a slope of the RGB+W gamma curve increases as compared to the RGB gamma curve. Accordingly, when the gray level is more than about the 150th level, a luminance difference between gray levels along the RGB+W gamma curve is larger than a luminance difference between gray levels along the RGB gamma curve. Thus, images with high gray levels greater than the 150th level are distinctly displayed.
However, as shown in FIG. 1, when the gray level is less about the 150th level, a luminance difference between the gray levels along the RGB+W gamma curve is smaller than a luminance difference between the gray levels along RGB gamma curve. Thus, images with low gray levels less than the 150th level are not distinctly displayed. Therefore, it is problematic that the difference between the gray levels along the RGB+W gamma curve is smaller than the difference between the gray levels along RGB gamma curve when the gray level is less than about the 150th level. For example, regions of an image having high gray levels, such as bright colors, are distinctly displayed, but regions of the image having low gray levels, such as dark colors, are not distinctly displayed.